Supercritical fluid extraction of metsulfuron methyl, sulfometuron methyl,and nicosulfuron from soils

Sulfonylurea herbicides are usually extracted from soils with batch liquid techniques. The objective of this study was to develop a general supercriti cal fluid extraction (SFE) procedure for sulfonylurea herbicides in soils. The procedure was optimized for metsulfuron methyl, and the parameters inve stigated included: SF-CO2 density, extraction time, and methanol modifier a ddition. Quantitative extraction could only be performed at high densities (i.e., 0.9 g ml(-1)) and with 2% (w/w) modifier addition. C-14-labeled mets ulfuron methyl, sulfometuron methyl, and nicosulfuron were extracted from s andy loam, silt loam, and clay loam soils spiked at two levels (0.4 and 4 m u g g(-1)) of herbicide. Under the conditions used, good recoveries of mets ulfuron methyl and sulfometuron methyl (75-89%) were obtained. However, nic osulfuron was difficult to extract (1-4%). The results show that an optimiz ed method cannot always be directly applied to similar compounds without fu rther method development.